Discharge lamp igniting circuit

ABSTRACT

A discharge lamp igniting circuit in a discharge lamp of short tube length and capable of being ignited only by pre-heating a filament thereof, comprising a stabilizer winding having a secondary winding; a switching element connected to the discharge lamp at a terminal of one filament of said discharge lamp which is not connected to a power supply; and a diode connected to said secondary winding to keep said switching element conductive for at least one cycle until the discharge lamp is started; said secondary winding of the stabilizer winding, said filament of the discharge lamp, said switching element and said diode forming a closed loop to promote pre-heating of the filament and energize the stabilizer winding throughout all cycles by a short-circuit current flowing through the secondary winding, the switching element and the diode. With such a discharge lamp igniting circuit, a kick voltage produced at a time of ignition of the discharge lamp can be well prevented to eliminate possible darkening of the discharge lamp at its end portions.

Shimizu et al.

[451 Sept. 18, 1973 DISCHARGE LAMP IGNITING CIRCUIT Inventors: Tetsuji Shimizu; Makoto lwalturn,

both of Nagoya City; Hiroshi Tanaka, Yoro-gun, all of Japan Kabushiki Kaisha Tokai Rika Denki Seisakusho, Aichi Pref., Japan Filed: Aug. 5, 1971 Appl. No.: 169,234

Assignee:

US. Cl. 315/94, 3l5/D1G. 5, 315/101, 315/105 Int.'Cl. H05b 39/00 Field of Search 315/D1G. 5, 94, 101, 315/105, 106, 107, 200, 206, 239, 243, 254

References Cited UNITED STATES PATENTS 12/1971 Miyajima 315/94 2/1972 Koyama et al 3l5/DlG. 5

Primary Examiner-Roy Lake Assistant Exnminer i awrence J Dahl V Attorney-Woodhams, Blanchard & Flynn I [57] ABSTRACT A discharge lamp igniting circuit in a discharge lamp of short tube length and capable of being ignited only by pre-heating a filament thereof, comprising a stabilizer winding having a secondary winding; a switching element connected to the discharge lamp at a terminal of one filament of said discharge lamp which is not connected to a power supply; and a diode connected to said secondary winding to keep said switching element conductive for at least one cycle until the discharge lamp is started; said secondary winding of the stabilizer winding, said filament of the discharge lamp, said switching element and said diode forming a closed loop to promote pre-heating of the filament and energize the stabilizer winding throughout all cycles by a shortcircuit current flowing through the secondary winding, the switching element and the diode. With such a discharge lamp igniting circuit, a kick voltage produced at a time of ignition of the discharge lamp can be well prevented to eliminate possible darkening of the discharge lampat its end portions.

8 Claims, 3 Drawing Figures PATENTED 1973 SHEEIIBFZ FIG SSS

INVENTORS PATENTED SEPI 8 I973 SHEU 2 Bf 2 Current flowing through 555, F1 D2 during negative half cycle L- ..1

Voltage acrou L0 Vohaqc w form acron siobi or winding Voltage ucrou lump Raver" block voliugl due to DD INVENTORS HTSZIJ/ SW/M/ZZ/ 1 DISCHARGE LAMP IGNITING CIRCUIT The present invention relates to a circuit for starting a discharge lamp such as a fluorescent lamp, capable of being instantaneously ignited only by preheating a filament thereof.

Usually, a discharge lamp such as a fluorescent lamp or the like may be started by applying preheating current to one of filaments which is a cathode of the lamp, to pre-heat it for emitting electrons from said cathode and applying a high voltage between the cathode and an anode of the other filament of the lamp to direct the electrons to the anode for inducing a glow discharge.

However, it is to be noted that, with a discharge lamp of short tube length, such as those lamps of power dissipation of watts, 8 watts, 6 watts, 4 watts etc., it is possible to start the discharge lamp only by a glow discharge produced at a cathode (i.e. an end are produced between cathode electrodes) by increasing a preheating current enough to promote emission of elec trons from the cathode.

The present invention has been made based on the above-mentioned fact andther'efor, it is an object of the present invention to provide an improved discharge lamp igniting circuit permitting a rapid and reliable start of discharge lamp, within several cycles after a powering on operation, by pre-heating the filaments of the lamp.

It is another object of the present invention to provide a discharge lamp igniting circuit capable of starting a discharge lamp only by pre-heating its filament, without applying any kick voltage, to effectively prevent possible darkening at the ends of the discharge lamp and consequently prolong the life-span thereof.

In accordance with the present invention, there is provided a discharge lamp igniting circuit in a discharge lamp of short tube length and capable of being ignited by pre-heating filaments thereof, comprising a stabilizer winding having a secondary winding, a switching element connected to the discharge lamp at a terminal of one filament of said discharge lamp which is not connected to a power supply; and a diode connected to said secondary winding to keep said switching element conductive for at least one cycle until the discharge lamp is started, said secondary winding of the stabilizer winding, said filament of the discharge lamp, said switching element and said diode forming a closed loop to promote pre-heating'of the filament and energize the stabilizer winding throughout all cycles by a short-circuit current flowing through the secondary winding, the switching element and the diode, thereby preventing a kick voltage from being producedat time of igniting the discharge lamp. Y

The invention will be better understood from the following discription taken in connection with the accompanying drawings in which:

FIG. 1 is a basic circuit diagram of a preferred embodiment of the present invention; a

FIG. 2 is a basic circuit diagram of another embodiment of the present invention; and

FIG. 3 is a diagram illustrating voltage and current waveforms at various points of the basic circuit shown in FIG. 1. r

Referring now to the drawings, particularly to FIG. 1, there is illustrated a preferred embodiment of the pres ent invention. Numeral E represents an A.C. power supply and L represents a stabilizer winding. Numeral FL designates a discharge lamp such as a fluorescent lamp, one of its filaments Fl being connected at its terminal near the power supply to one terminal thereof through the stabilizer winding L. Connected between a terminal of the filament Fl remote from the power supply and a terminal of another filament F, remote from the power supply are connected in series a switching element, more particularly a two-terminal bidirectional thyristor SSS, and a diode D1. The terminal of the filament F, near the power supply is connected to the other terminal of the power supply.

A diode D, has an anode connected to the junction point of the thyristor SSS and the diode D,, and a cathode connected to a center tap of the stabilizer winding L. A capacitor C serves as an anti-noise capacitor.

The operation of the above circuit will now be explained with reference to FIG. 3. With the power supply ON, the thyristor SSS is turned on at a breakdown voltage V, in a positive half cycle so that the filaments F, and F, of the discharge lamp FL are pre-heated by a current flowing from the power supply E and back thereto, through the stabilizer winding L, the filament F,, the thyristor SSS, the diode D,, the filament F2.

Thus, the thyristor SSS starts its conduction from a point a (FIG.3) in the positive half cycle while a preheating current I, flows with lagging phase. Therefore,

when the voltage amplitude becomes zero, the preheating current I, still flows and when the voltage amplitude swings to the negative a secondary winding L of the stabilizer winding L is short-circuted by the closed loop comprising the filament F,, the thyristor SSS and the diode D, since the latter is forward-biased. As a result, the short-circuit current I, flows from the secondary winding L through the filament F,, the thyristor SSS, the diode D,, back to the secondary winding L and the filament F, is pre-heated until the next positive half cycle begins.

On the other hand, the pre-heating current flowing through the diode D, is terminated at a point b in FIG.3,' causing an interruption of preheating of the filament F2.

Thus, since the closed loop comprising the secondary winding L,, the filament F,, the thyristor SSS and the diode D, is isolated from the power supply E, the shortcircuit current I, flowing from the power supply through the diode D, at the negative half cycle, is interrupted. The magnetic flux produced in the secondary winding L, by the short-circuit current I, is not dissipated in the loop at once but decreases gradually. Resultantly, the short-circuit current I, in the loop also decays gradually and if it continues to flow until the next positive half cycle, the thyristor SSS is kept in conduction since the voltage does not drop to V,, thus maintaining conductive state for two cycles.

Thus, a current flows through the stabilizer winding L throughout the cycles and the value di/dt does not become indefinite. No kick voltage is, therefore, produced in the stabilizer winding L. is selected to be higher than the above two voltages.

It is seen from. FIG.3 that a reverse blocking voltage substantially equal to that of the power supply E is applied to the ends of the discharge lamp by the diode D,. Thus, a half wave discharge circuit is completed with the filament F, being a cathode and the filament F, being an anode. Since both filaments F, and F,, especially F,, have been pre-heated enough to produce endarc, the discharge lamp is started.

Once the discharge lamp has been started, the voltage thereacross drops to a discharge sustain voltage. Since the secondary voltage appeared across the secondary winding L, of the stabilizer winding L also drops, the discharge lamp circuit becomes independent after it has been started, provided that the breakdown voltage V, of the thyristor SSS lS SELECTED TO BE HIGHER THAN THE ABOVE TWO VOLTAGES.

FIG. 2 illustrates a modified circuit in which the autotransformer L in FIG.1 is replaced by an two-winding transformer L. The operation of the circuit of P162 is the same as that described in connection with FIG.1.

The switching element used in the above embodiments should not be limited to a two-terminal bidirectional thyristor SSS but it may be of any type of thyristor such as SCR, TRIAC, SUS or the like.

As described above, according to the present invention, the circuit is closed at a certain phase in the first cycle after powering on and the short-circuit current is maintained during and after the second cycle through the switching element, the diode, the secondary winding and one of the filaments. Therefore, in a discharge lamp of short tube length, or, a discharge lamp having power dissipation of watts or less, discharge may instantaneously start to light the lamp. On the other hand, since current flows through the stabilizer winding throughout the cycles, no kick voltage is produced across the stabilizer winding, whereby darkening at the ends of the discharge lamp is effectively eliminated and the life of the lamp can be prolonged.

What is claimed is:

1. In a discharge lamp of short tube length responsive to an AC power supply voltage thereacross for being ignited by pre-heating a filament thereof and without application of a kick voltage thereto, a discharge lamp igniting circuit comprising a stabilizer winding connected in circuit with the power supply and terminals of the filaments of the lamp and having a secondary winding; a switching element having a breakdown voltage and connected to the discharge lamp at a further terminal of one filament of said discharge lamp for conducting through said stabilizer winding due to first half cycles of said power supply; and adiodeconnected to said secondary winding to keep said switching element conductive for at least one cycle until the discharge lamp is started; said secondary winding of the stabilizer winding, said one filament of the discharge lamp, said switching element and said diode forming a closed loop to promote pre-heating of the filament and maintain energization of the stabilizer winding throughout all cycles prior to lamp ignition by a current flowing through the secondary winding, the switching element and the diode, thereby preventing a kick voltage from being produced at a time of igniting the discharge lamp.

2. A discharge lamp igniting circuit as claimed in claim 1 wherein said secondar winding is an autotransfonner winding.

3. A discharge lamp igniting circuit as claimed in claim 1 wherein said secondary winding is a winding of a two-winding transformer.

4. A discharge lamp igniting device as claimed in claim 1 wherein said switching element is a thyristor.

5. A discharge lamp igniting switch as claimed in claim 1 wherein said discharge lamp has power dissipation of 10 watts or less.

6. In a discharge lamp igniting circuit for a lamp of short tube length and capable of being ignited by preheating a filament thereof at the rated voltage of the lamp and without a kick voltage applied thereto, such lamp having a pair of filaments, each filament having a pair of terminals, the combination comprising:

a stabilizer winding and means connecting same in circuit with a terminal of each lamp filament to an AC power supply for maintaining the lamp conductive after ignition, said stabilizer winding having a secondary winding; thyristor switching element and a first diode connected end to end between said filaments and to the remaining terminals thereof and being a portion of the flow path of preheating current through said filaments and stabilizer winding in one portion of a cycle of said power supply;

a second diode connecting said end of said switching element to said secondary winding.

7. A discharge lamp igniting device as claimed in claim 6, in which said diodes connect back to back at the ends thereof connected to said switching element.

8. A discharge lamp igniting device as claimed in claim 6, in which said switching element, the filament connected thereto, said second diode and said secondary winding define a closed series loop for flowing current therethrough for the remaining portion of said cycle, whereby preheating current flows continuously through said switching element during preheating'and ignition of said lamp.

O i i i t 

1. In a discharge lamp of short tube length responsive to an AC power supply voltage thereacross for being ignited by pre-heating a filament thereof and without application of a kick voltage thereto, a discharge lamp igniting circuit comprising a stabilizer winding connected in circuit with the power supply and terminals of the filaments of the lamp and having a secondary winding; a switching element having a breakdown voltage and connected to the discharge lamp at a further terminal of one filament of said discharge lamp for conducting through said stabilizer winding due to first half cycles of said power supply; and a diode connected to said secondary winding to keep said switching element conductive for at least one cycle until the discharge lamp is started; said secondary winding of the stabilizer winding, said one filament of the discharge lamp, said switching element and said diode forming a closed loop to promote pre-heating of the filament and maintain energization of the stabilizer winding throughout all cycles prior to lamp ignition by a current flowing through the secondary winding, the switching element and the diode, thereby preventing a kick voltage from being produced at a time of igniting the discharge lamp.
 2. A discharge lamp igniting circuit as claimed in claim 1 wherein said secondar winding is an autotransformer winding.
 3. A discharge lamp igniting circuit as claimed in claim 1 wherein said secondary winding is a winding of a two-winding transformer.
 4. A discharge lamp igniting Device as claimed in claim 1 wherein said switching element is a thyristor.
 5. A discharge lamp igniting switch as claimed in claim 1 wherein said discharge lamp has power dissipation of 10 watts or less.
 6. In a discharge lamp igniting circuit for a lamp of short tube length and capable of being ignited by preheating a filament thereof at the rated voltage of the lamp and without a kick voltage applied thereto, such lamp having a pair of filaments, each filament having a pair of terminals, the combination comprising: a stabilizer winding and means connecting same in circuit with a terminal of each lamp filament to an AC power supply for maintaining the lamp conductive after ignition, said stabilizer winding having a secondary winding; a thyristor switching element and a first diode connected end to end between said filaments and to the remaining terminals thereof and being a portion of the flow path of preheating current through said filaments and stabilizer winding in one portion of a cycle of said power supply; a second diode connecting said end of said switching element to said secondary winding.
 7. A discharge lamp igniting device as claimed in claim 6, in which said diodes connect back to back at the ends thereof connected to said switching element.
 8. A discharge lamp igniting device as claimed in claim 6, in which said switching element, the filament connected thereto, said second diode and said secondary winding define a closed series loop for flowing current therethrough for the remaining portion of said cycle, whereby preheating current flows continuously through said switching element during preheating and ignition of said lamp. 